Products made from a fibrous web are used for a variety of purposes. For example, paper towels, facial tissues, toilet tissues, napkins, and the like are in constant use in modern industrialized societies. The large demand for such paper products has created a demand for improved versions of the products. If the paper products such as paper towels, facial tissues, napkins, toilet tissues, mop heads, and the like are to perform their intended tasks and to find wide acceptance, they must possess certain physical characteristics.
Among the more important of these characteristics are strength, softness, and absorbency. Strength is the ability of a paper web to retain its physical integrity during use. Softness is the pleasing tactile sensation consumers perceive when they use the paper for its intended purposes. Absorbency is the characteristic of the paper that allows the paper to take up and retain fluids, particularly water and aqueous solutions and suspensions. Important not only is the absolute quantity of fluid a given amount of paper will hold, but also the rate at which the paper will absorb the fluid.
Through-air drying papermaking belts comprising a reinforcing element and a resinous framework, and/or fibrous webs made using these belts are known and described, for example, in the following commonly assigned U.S. patents, the disclosures of which are incorporated herein by reference: U.S. Pat. No. 4,514,345, issued Apr. 30, 1985 to Johnson et al.; U.S. Pat. No. 4,528,239, issued Jul. 9, 1985 to Trokhan; U.S. Pat. No. 4,529,480 issued Jul. 16, 1985 to Trokhan; U.S. Pat. No. 4,637,859 issued Jan. 20, 1987 to Trokhan; U.S. Pat. No. 5,098,522, issued Mar. 24, 1992 to Smurkoski, et al.; U.S. Pat. No. 5,245,025 issued Sep. 14, 1993 to Trokhan et al.; U.S. Pat. No. 5,260,171, issued Nov. 9, 1993 to Smurkoski et al.; U.S. Pat. No. 5,275,700, issued Jan. 4, 1994 to Trokhan; U.S. Pat. No. 5,328,565, issued Jul. 12, 1994 to Rasch et al.; U.S. Pat. No. 5,334,289, issued Aug. 2, 1994 to Trokhan et al.; U.S. Pat. No. 5,431,786, issued Jul. 11, 1995 to Rasch et al.; U.S. Pat. No. 5,496,624, issued Mar. 5, 1996 to Stelljes, Jr. et al.; U.S. Pat. No. 5,500,277, issued Mar. 19, 1996 to Trokhan et al.; U.S. Pat. No. 5,514,523, issued May 7, 1996 to Trokhan et al.; U.S. Pat. No. 5,527,428 issued Jun. 18, 1996 to Trokhan et al.; U.S. Pat. No. 5,554,467, issued Sep. 10, 1996, to Trokhan et al.; U.S. Pat. No. 5,566,724, issued Oct. 22, 1996 to Trokhan et al.; U.S. Pat. No. 5,624,790, issued Apr. 29, 1997 to Trokhan et al.; U.S. Pat. No. 5,628,876 issued May 13, 1997 to Ayers et al.; U.S. Pat. No. 5,679,222 issued Oct. 21, 1997 to Rasch et al.; U.S. Pat. No. 5,714,041 issued Feb. 3, 1998 to Ayers et al.; U.S. Pat. No. 5,900,122 issued May 4, 1999 to Huston; and U.S. Pat. No. 5,948,210 issued Sep. 7, 1999 to Huston.
In the aforementioned belts of prior art the resinous framework is joined to the fluid-permeable reinforcing element (such as, for example, a woven structure, or a felt). The resinous framework may be continuous, semi-continuous, comprise a plurality of discrete protuberances, or any combination thereof. The resinous framework extends outwardly from the reinforcing element to form a web-side of the belt (i. e., the surface upon which the web is disposed during a papermaking process), a backside opposite to the web-side, and deflection conduits extending therebetween. The deflection conduits provide spaces into which papermaking fibers deflect under application of a pressure differential during a papermaking process. Because of this quality, such papermaking belts are also known in the art as “deflection members.” The terms “papermaking belt” and “deflection member” may be used herein interchangeably.
Papers produced on such deflection members, disclosed in the aforementioned patents, are generally characterized by having at least two physically distinct regions: a region having a first elevation and typically having a relatively high density, and a region extending from the first region to a second elevation and typically having a relatively low density. The first region is typically formed from the fibers that have not been deflected into the deflection conduits, and the second region is typically formed from the fibers deflected into the deflection conduits of the deflection member. The papers made using the belts having a continuous resinous framework and a plurality of discrete deflection conduits dispersed therethrough comprise a continuous high-density network region and a plurality of discrete low-density pillows (or domes), dispersed throughout, separated by, and extending from the network region. The continuous high-density network region is designed primarily to provide strength, while the plurality of the low-density pillows is designed primarily to provide softness and absorbency. Such belts have been used to produce commercially successful products, such as, for example, Bounty® paper towels, Charmin® toilet tissue, and Charmin Ultra® toilet tissue, all produced and sold by the instant assignee.
Typically, certain aspects of absorbency of a fibrous structure are highly dependent on its surface area. That is, for a given fibrous web (including a fiber composition, basis weight, etc.), the greater the web's surface area the higher the web's absorbency. In the structured webs, the low-density pillows, dispersed throughout the web, increase the web's surface area, thereby increasing the web's absorbency. However, increasing the web's surface area by increasing the area comprising the relatively low-density pillows would result in decreasing the web's area comprising the relatively high-density network area that imparts the strength. That is, increasing a ratio of the area comprising pillows relative to the area comprising the network would negatively affect the strength of the paper, because the pillows have a relatively low intrinsic strength compared to the network regions. Therefore, it would be highly desirable to minimize the trade-off between the surface area of the high-density network region primarily providing strength, and the surface area of the low-density region primarily providing softness and absorbency.
Now, it has been discovered that the areas of the high-density region and the low-density region can be effectively de-coupled in a fibrous structure, e. g., that the surface area of the fibrous structure may be increased without sacrificing the strength of the fibrous structure. Specifically, it has been discovered that the surface area of the relatively low-density and absorbent pillows can be sufficiently increased, without decreasing the area of the relatively high-density network, by forming a novel fibrous structure using a deflection member of the present invention.
Accordingly, the present invention provides a novel strong, soft, and absorbent fibrous structure and a process for making such a fibrous structure. More specifically, the present invention provides a fibrous structure that has at least two regions: a first region having a first elevation and a second region extending from the first region to define a second elevation, the second region having an increased surface area that enhances absorption qualities of the fibrous structure.
The present invention further provides a fibrous structure wherein the second region comprises fibrous domes and fibrous cantilever portions laterally extending from the domes. The fibrous cantilever portions increase the surface area of the second region and form, in some embodiments, pockets comprising substantially void spaces between the fibrous cantilever portions and the first region. These pockets are capable of receiving additional amounts of liquid and thus further increase absorbency of the fibrous structure.
The present invention also provides novel deflection members useful for making such structured fibrous structures. More specifically, the present invention provides deflection members comprising a patterned framework having suspended portions that form voids into which the fibers can be deflected during a process for making the fibrous structure of the present invention, to form the fibrous cantilever portions.
The present invention further provides processes for making such deflection members. In one embodiment, such a deflection member comprises a multi-layer framework formed by at least two layers joined together in a face-to-face relationship. Each of the layers has a deflection conduit portion. The deflection conduit portion of one layer is fluid-permeable and positioned such that portions of that layer correspond to the deflection conduits of the other layer and thus comprise a plurality of suspended portions.
In another embodiment, such a deflection member comprises a single-layer framework wherein the suspended portions are formed by curing a layer of a curable material through a novel mask of the present invention, comprising regions of differential opacities.
In still another embodiment, the deflection member can be made by curing a coating of the curable material through a novel mask of the present invention, comprising opaque regions and transparent regions, and a three-dimensional topography.
The present invention further provides novel masks that can be used in a process for selective curing of a curable material, such as, for example, a photosensitive resinous material. Such masks can also be used in making deflection members of the present invention. More specifically, the present invention provides a mask having a pattern of transparent regions and opaque regions, the opaque regions comprising differential opacity.
The present invention also provides a mask in which the opaque regions comprise a gradient opacity that gradually changes in at least one direction. The present invention further provides a mask having a combined pattern comprising a pattern of the transparent/opaque regions and a three-dimensional pattern of protrusions extending from at least one side of the mask. The present invention also provides processes for making the masks of the present invention.